This research is directed toward development of an ultrasonic ventilometer with measurement accuracy suitable for clinical applications in O2 consumption studies, critical care monitoring, and pulmonary function testing. Methods include integrating the knowledge of sound/fluid flow interactions, diffraction theory, acoustic transducers, and contemporary signal processing. Computer models of each phase will be generated and compared with experimental data to determine the accuracy and predictive value of the models. A laboratory prototype flowmeter will be constructed and tested both statically and dynamically using gases and temperatures consistent with clinical norms and extremes. Information thus gained will be used to design a clinical prototype which will receive evaluation in both critical care and screening environments.